1. Field of the Invention
This invention relates to a sprinkler, which is closed by means of a valve disc by pressure sealing.
2. Description of the Prior Art
Sprinklers must remain tight against varying water pressures over decades, under varying atmospheric and thermal conditions, but must open without sticking as soon as they are triggered. The usually thermal triggering devices must respond as sensitively and reliably as possible.
The majority of conventional sprinkler designs with pressure sealing make use of a relatively stiff valve disc, which is pressed down by a resilient support onto a rigid valve seating. The resilient support includes the trigger member and some intermediate members, which together constitute the thermal trigger, and also includes the sprinkler body. While a certain spring property is necessary, in order to compensate for the influence of the differing temperature strain and bedding down of the individual components during decades of continuous use, the exact location of the spring in the support has varied considerably. In some prior sprinkler heads, the resiliency, or spring, is obtained in the sprinkler body which is integral with the valve seat, and in other sprinkler heads, the resiliency is obtained in parts related to the thermal trigger. Where glass bulbs are used as the trigger member, with their very different temperature expansion by comparison with metals, a special spring packet is usually also required. Such prior art provides for the resiliency at locations away from the actual closure which traverses the valve seat.
Pressure seals are simple in construction and impose relatively easy demands upon the sealing material by comparison with self-sealing chamber seals, for example comprising O-rings, which in addition demand permanently elastic properties of the material.
The strength of thermal trigger members in sprinklers should be designed essentially according to the expected permanent load, which may be carried for many years, since the permissible endurance strength of the usual trigger members with eutectic solders or glass bulbs amounts to only a small portion of their short-term load-bearing capacity.
In said prior art sprinkler designs, which provide for the necessary resiliency at a location away from the closure which traverses the valve opening, and which in their sealing action are comparable to a spring-loaded safety valve, the load applied to the support and thus to the trigger member at operating pressure (up to 12.5 bars) is as high as at the maximum test pressure (up to more than 60 bars), that is the leakage pressure at which the valve disc commences to lift as a whole. In other words, there is no relief or reduction in pressures carried by the support and thermal trigger under normal operating conditions as compared to the conditions to resist extreme test or leak pressures which will be encountered only momentarily or for short periods. The permanent load corresponds to the maximum occurring force, and especially as a result powerful and thus heavy or complicated triggering devices are necessary.
With other sprinkler designs with chamber seals it is possible, as a result of the self-sealing action, to reduce the permanent load considerably by comparison with the loading at maximum test pressure. Nevertheless, permanently elastic materials are necessary, which hitherto have not satisfied all the requirements throughout the entire operating range of the sprinkler.
Another form of construction (German Patent No. 1,258,278) achieves a reduced permanent load by utilising a resilient valve seating projecting in the form of a collar, and additionally compressed by the hydraulic forces. This form of construction, however, is complicated and expensive to manufacture.